Synchronous alternating-current motor.



No. 707,389. Patented Aug. I9, I902.

A. GHURCHWARD. SYNGHRONOUS ALTERNATING CURRENT MOTOR.

(Application filed Oct. 1, 1898. Renewed May 1, 1901.) (No Model.) 2Sheets-Sheet l.

FIG. 7.

WITNESSESZ INVENTORZ & Mm @M/u/W T i NORM PETERS cu, PNOTO-LITNO\vAsHxNmoN, D c.

No. 707,389. Patented Aug. [9, I902.

A.- CHURCHWARD. SYNCHRUNUUS ALTEBNATING CURRENT MOTOR.

(Application filed Oct. 1, 189B. Renewed May 1, 1901.)

2 Sheets-Sheet 2.

(No Model.)

INVENTOR:

WITNESSES:

UNITED STATES ALEXANDER OHUROHWARD,

PATENT OFFICE.

OF FORT WAYNE, INDIANA.

SYNCHRONOUS ALTERNATlNG-CURRENT MOTOR.

$PECIFICATION forming part Of Letters Patent N0. 707,389, dated August19, 1902. Application filed October 1,1898. Renewed May 1, 1901. flerialNo. 58,364. (No model.)

To all whom it may concern.-

Be it known that I, ALEXANDER CHURCH- WARD, a citizen of the UnitedStates, residing at Fort Wayne, in the county of Allen and State ofIndiana, have invented certain new and useful Improvements inSynchronous Alternating Motors, of which the following is aspecification.

My invention relates to dynamo-electric machines, and principally tomotors, in connection with which the invention will be described.

The object of this invention is to overcome the difficulties encounteredin operating synchronous alternating-current dynamos, particularlymotors, when the dynamo or generator supplying the motor fluctuates inspeed in different parts of a revolution, as occurs when the generatoris driven by an engine the propulsive thrust of which varies atdifferent periods of each revolution.

It is commonly said that the speed of two alternating dynamos that arerun 'in synchronism is definitely fixed by their relative numbers offield-poles, so that the two armatures make the same number ofalternations per minute. It is in addition practically important thatthe two armatures maintain the same relative speed at all times. Thus ifthe generator is driven (by direct connection or otherwise) from anengine the speed of which varies at different parts of a revolution, sothat the same variations in speed are communicated to the generator, andis connected in circuit with a second machine which runs at practicallyuniform speed (by having a very heavy fly-wheel or by its armatureacting as a fly-wheel) it will follow that thephases of the two machineswill be at times coincident, while at other times one machine may be inadvance of or behind the other. The elfect of a given difference ofspeed depends largely on its relation to the number of poles of thealternator. Thus,for example,the speed variation may be such that at oneinstant one armature is one-hundredth of a revolution in advance of theother, while at another instant it is an equal amount behind the other,and in such case if the machine have one hundred poles then theelectromotive forces of the armatures will at one instant agree inphase, while at the next instant they will be of exactly wrong phase,with the result that a heavy current will flow through the machines. If,however, to take the contrary extreme case, the two alternators betwo-pole machines, then an advance of only one-hundredth of a revolutionof one armature rela tively to the other will cause so trifling adifference in the electromotive forces as to produce little or noappreciable effect-that is to say, the effect is only one-fiftieth ofthat produced in the former case.

A sychronous motor tends to run at a uniform speed, since its revolvingelement acts as a fly-wheel. ,This tendency is especially marked whenrunning under light load. If the generator speed fluctuates, itselectromotive force will sometimes be in advance of and sometimes behindthat of the motor, and the diflerence between the two will cause thecurrent between the machines to fluctuate in strength, being at itsminimum when the electromotive forces of the two machines are directlyopposite in phase and in maximum when there is the greatest variationfrom this condition. A sychronous motor that is connected to a circuiton which the rapidity of alternation fluctuates at regular intervalstends to pump that is, its armature runs sometimes a little faster andsometimes a little slower than the generator-with the result of causinga beating sound in the motor. Such pumping or beating action is usuallyindicative of some irregularity in the circuit feeding the motor. Thisirregularity may consist of variations either in speed or inelectromotive force. The variation in speed of the generator tends tocause a corresponding variation in the speed of a sychronous motor. Themotor cannot, however, assume instantly the speed required by the newspeed of the generator. When the speed of the generator increases, themotor-armature begins to increase in speed; but by reason of its laggingthe motor receives an increased current, because its armature is not innormal position for the new frequency and because additional current isrequired for supplying the energy necessary for increasing its speed.This additional current produces a difference of magnetism of the field,which must again be altered when the generator speed decreases below theaverage. The motor is therefore undergoing a slight variation in speed,which seeks to approximate to, but does not exactly correspond with,that of the generator. This pumping or rocking, however, will almostentirely disappear when even a small load is put on the motor. It hasheretofore been the custom to weaken the field of a synchronous motorwhen it was found to pump. The effect of this is to lower theelectromotive force of the motor, thereby putting an artificial load onthe armature, which, however, while it reduces the pumping has thedisadvantage of reducing the electromotive force of the generator and ofupsetting the line. To overcome this defect and avoid interference withthe line is the purpose of my invention.

According to this invention I apply on the shaft of the motor or on ashaft driven therefrom a fly-wheel of suitable weight, whichinstead ofbeing fixedly connected to the motor in the usual manner is connectedthereto through the medium of a yielding connection, which may be africtional connection, but is preferably a spring connection, in whichcase the fiy-wheel has such freedom of motion with reference to thearmature that the latter can.

lags behind, thereby putting a slight load on the motor, and then whenthe generator slows down the motor-armature tends to run slower, whilethe fly-wheel tending to run at a uniform speed catches up with themotor-shaft and forces it ahead or resists its tendency to slow down,thereby again putting a slight load on the motor. I have already statedthat putting a slight load on a synchronous motor extinguishes thepumping effect, this being equally true whether it is electrical, byweakening the field and taking extra current, or is mechanical, bythrowing some additional work upon the motor. I The yieldinglyconnectedfly-wheel provided by my invention is of the latter order and has theeffect of causing the motor to run without any pumping. Inasmuch as theload imposed by the fiy-wheel is felt only at the instants when thevariation in speed occurs, its effect in correcting the pumping isaccompanied by less on the line 3 3 in Fig. 4. Fig. 4: is a trans versesection of the fly-wheel and collar on the line 4 4 in Fig. 3. Fig. 5 isa face view of the collar, and Fig. 6 a transverse section thereof onthe line 6 6 in Fig. 5. Fig. 7 is a diametrical section of a modifiedconstruction of fiy-wheel. Fig. 8 is a diagrammatic elevationillustrating a modification.

According to Fig. 1, let G designate an alternating current generator,(single or multi phase,) and a a the circuit fed therefrom. I have shownthis generator as driven by a direct-connected steam-engine E. M and Mare synchronous motors. The motors may have the same number of poles asthe generator or a different number, as is well understood. The motor M,I have shown as directly connected to the circuit a, while the motor M,I have shown as connected through a transformer T. To avoid complicationin the diagram, I have not shown the means for exciting the field-magnets of the generator and motors and have also omitted all electricalaccessories, such as starting-switches, &c.

In Fig. 2 I have shown an alternating motor of well-known type, of whichf is the field-magnet, A is the armature, bis the armature-shaft, ccarethe collector-rings, and d d are the brushes leading the alternatingcurrent into these rings. I have shown this machine as constructed witha commutator e for feeding continuous current to brushes g g for thepurpose of exciting the field-magnets;

but these exciting connections not being mamounted a fly-wheel F. Thepreferred construction is that shown in Figs. 3 to 6, where thefly-wheel F is loosely mounted upon a sleeve B, which itself is keyed orotherwise fixed upon the shaft. Attached to the shaft is a collar 0,which is preferably made in one piece with the sleeve B and which hasone or more (preferably two) projections h h. The fly-wheel haspreferably two arc-shaped chambers t' t' for receiving these projectionsand for inclosing springs S S, preferably coiled or helical springs, asbest shown in Fig. 3. The opposite ends of these springs are socketed inrecessesj and 7c, the former being formed in the projections h and thelatter being formed at the ends of the chambers 'i. The springs arearranged in one or more pairs, so as to afford elastic and resilientconnections for resisting relative movement of the fly-wheel and shaftin either direction. The ends of the chambers 't' are formed at themouths of the sockets with projections or shoulders m, which constitutestops adapted to encounter the projections h to limit the relativedisplacement of the fly-wheel and shaft. This displacement should besufficient so that if the fly-wheel were held stationary the shaft couldbe turned enough to displace the armature from one field-pole to thenext.

The stops limit the compression or stress which may be applied to thesprings S S, and thereby prevent overstraining' the springs.

My invention is not confined to the exact construction thus described,since any construction by which the fly-wheel is mounted to turnindependently on the shaft and is connected thereto by a yielding orelastic connection adapted to resist movement of the fly-wheelrelatively to the shaft will be within my invention. Any kind orarrangement of spring may be employed, it being understood that thesprings may be arranged to act in either tension or compression or bytorsion, or the springs may be simply yielding cushions.

Fig. 7 illustrates a modification embodying my invention. Here theyielding connection between the fly-wheel and shaft instead of beingelastic is frictional. In effect the flywheel is mounted on the shaftthrough the medium of a friction-brake. The sleeve B is fixed on theshaft, as before described, and formed on one side with a flange orcollar 71, while its opposite end receives a detachable and adjustablecollar p, connected, preferably, by screwing it upon-the threaded end ofthe sleeve, the collar being split on one side and its split portionprovided with a clamping-screw g, by which to contract the collar uponthe screw-threads to lock it in place in awell-known manner. The hub ofthe flywheel F is confined between the collars n and p, friction disksor washers r 7', preferably of rawhide, being placed against oppositefaces of the hub and metal washers s 8 being preferably placed outsideof these disks against the respective collars. The collar n has a seriesof sockets n, in which are confined stiff springs t 25, which tend topress the plate 5 against the hub of the fly-wheel, and thereby generatea degree of friction between the fiy-Wheel and sleeve, the frictionalretardation being adjustable by screwing up more or less the collar 1).A pin it, entering a hole in the disk 9', compels the latter to turnwith the sleeve.

The construction last described enables the motor-shaft to turnindependently of the flywheel, but resists this turning in eitherforward or backward direction to an extent dependent upon the amount offriction generated in the friction brake, and it is the amount of thisfriction that determines the load that the fly-wheel imposes upon themotor. The power expended in overcoming this friction is of course lost,but as this loss occurs only when the fluctuations in speed occurinstead of continuously, as when a mechanical load is put upon themotor, this loss is greatly reduced.

With the construction first described,where the yielding connectionbetween the fly-wheel and shaft consists of springs, the load imposedduring periods of speed variation is (in addition to unavoidablefriction) proportional to the compression of the springs, and thiscompression during the period of lagging is given back by the expansionof the springs during a succeeding period of acceleration, so that theload necessary to suppress pumping is economized.

Instead of applying the fly-wheel directly on the motor-shaft it may beapplied on any shaft driven by the motor. Thus in Fig. 8 I have shownthe motor belted to a countershaft 1) and the fiy-wheel F carried onthis counter-shaft, the construction being otherwise exactly the same asbefore described.

Where a rotary transformer is used for converting an alternating to adirect current, there is some pumping action, as before described, andmy invention is applicable in the same manner. Since such rotarytransformer involves a synchronous motor as one of its elements, it willbe understood that wherever such motor is herein referred to thiselement of a rotary transformer will be understood as included to thesame effect as though in each instancel had referred to a synchonousmotor or rotary transformer.

It will be observed that I have provided a new combination wherein arotating element is connected with the load through the agency of meansthat effects a yielding connection between the load and rotatingelement.

I claim as my invention the following-defined novel features,substantially as hereinbefore specified, namely:

1. The combination with a synchronous motor of a fly-wheel driventhereby through the medium of a yielding connection for producing theeffect described.

2. The combination with asynchronous motor of a fly-wheel mounted on itsshaft and driven thereby through the medium of a yielding connection.

3. The combination with a synchronous motor of a fly-wheel driventhereby, free to turn on its driving;shaft,and a yielding connectionbetween such fly-wheel and the motor, for producing the effectdescribed.

4. The combination with a synchronous motor of a fly-wheel driventhereby, free to turn on its driving-shaft, and springs interposedbetween the fly-wheel and shaft for producing the effect described.

5. The combination with a synchronous motor of'a fiy-wheel driventhereby, free to turn on its driving-shaft, a collar fixed to saidshaft, and springs constituting a yielding connection between thefly-wheel and collar.

6. The combination with a synchronous motor of a fly-wheel driventhereby free to turn on its driving-shaft,a collar fixed to said shaft,springs constituting a yielding connection between the fly-wheel andcollar, and a stop to limit the strain on said springs.

7. The combination with a synchronous motor of a fiy-wheel F driventhereby, a collar 0 fixed on the driving-shaft and having projections hh, and springs S S interposed between said projections and thefly-wheel.

S. The combination with a synchronous mo tor of a fly-wheel F driventhereby having arc-shaped chambers it, a collar fixed on thedriving-shaft and having projections h 7t projecting into said chambers,and springs S S interposed between said projections and the fiy-wheeland inclosed in said chambers.

9. The combination with a synchronous motor of a fly-wheel F driventhereby, a collar C fixed on the driving-shaft and having projec- 1Otions it h, and springs S S interposed between said projections and thefly-Wheel, and said fly-wheel and collar formed with mutuallyabuttingstops to limit the compression of said springs.

10. A synchronous motor and a load tending to maintain speedindependently of the motor and coupled therewith by a yieldingconnection.

1].. A synchronous motor and a load therefor tending to maintain speedindependentlyof the motor and provided with means for affording ayielding engagement between thesame and the said machine.

12. In a system of electrical distribution, the combination with agenerator of alternating currents, of a motor supplied with current fromthe generator, a load for the motor tending to maintain speedindependently of the motor, and means whereby the said load isyieldingly connected with the motor, substantially as described.

13. In a system of electrical distribution,

the combination with a generator of alternating currents, of a motorsupplied with ourtent from the generator, 2. load for the motor 3 5tending to maintain speed independently of the motor, and springmechanism whereby said load is yieldingly connected with the motor,substantially as described.

14.. The combination with a synchronous 4o dynamo-electric machine,of afly-Wheel driven thereby through the medium of a yieldingconnection,forproducing the effect described.

15. The combination with a synchronous dynamo-electric machine, of aload operated thereby through the medium of a yielding connection, saidload tending to maintain speed independently of the dynamo.

16. The combination with a rotary converter, of a fly-wheel driventhereby through the medium of a yielding connection for producing theeffect described.

17. The combination with a rotary converter, of a load operated therebythrough the medium of a yielding connection, said load tending tomaintain speed independently of the converter.

In witness whereof I have hereunto signed my name in the presence of twosubscribing witnesses.

ALEXANDER CHURCHIVARD. lVitnesses:

CHARLES C. MILLER,

JAMES J. W001).

